In a similar prior-art device of this class as described in West German Offenlegungsschrift (Laid-open Document) DE-OS 2,342,615, which serves to convert a stack of paper sheets into a continuous-type stream, an essentially vertical, oscillatingly suspended gripper belt, which is joined by a feed section at the top, is arranged in the end zone of the guiding device rising obliquely in the direction of feed for the sheet stack. The support element of this gripper belt consists of a plurality of plate pairs, which are connected to one another by shafts in the manner of a plate link articulated chain. A pressing belt is also in spring-mounted contact with the beginning of the feed section and forms, with the gripper belt, a wedge-shaped intake for the paper sheet pulled off from the stack. The pressing belt is in spring-mounted contact with the upper end of the gripper belt. Because of the oblique position of the support surface of the guiding device and the oblique setting of the sheets of the stack, which is sloped away from the gripper belt, it is achieved that the oscillatingly suspended gripper belt is pressed against the front side of the stack and is kept in frictionally engaged connection with the foremost sheet due to the force component of its own weight, which extends in parallel to the plane of the stack. However, because of this oblique position of the stack plane, it is also necessary to arrange a support, which is connected to the conveyer belt and by which the replenishing of sheets is made difficult, on the rear side of the stack.
A similar device for decollating sheets of paperboard, cardboard, sheet metal, or the like, from a stack is also known from West German patent No. DE-PS 806,139. In this document the sheets removed from the stack can be fed into a further processing machine. The sheets stand, slightly sloped in the forward position, on a link belt moving in the forward direction in an oblique plane with periodic strokes. To decollate the sheets, a picker device consisting of controlled suction nozzles is arranged in front of the front side of the stack, which moves the sheets one by one in the upward direction and transfers them to a guide web arranged above the stack. By the guide web, the sheets are brought into the horizontal direction and transferred to the processing machine. Adjacent the suction nozzles, the picker device has a plurality of registering straps. These registering straps are arranged movably in the upward and downward directions in the decollation plane and are provided with adjustable carriers. The adjustable carriers support the suction nozzles during the upward movement of the actually foremost sheet by ripping under the actually foremost sheet. A horizontal, rotatable roller, around which the upper section of the actually foremost sheet is bent downward and thus detached from the stack by the suction nozzles, which are arranged above the said roller and are movable both horizontally and in the upward and downward directions, is arranged tangentially to the decollation plane of the picker device above the registering straps in the upper half of the stack height. To support this detachment, blow nozzles are also provided in the upper area of the stack. Aside from the fact that the design of such a device is complicated and expensive, it is not possible to achieve a high feed capacity with it.
Another prior-art feed device for sheet-like parts is described in CH 670,441 A5 and is provided with a horizontal feed conveyer for receiving a sheet stack. At the feed end of the sheet stack a lifting device is located, which consists of at least two conveyer belts arranged relative to one another and guided such that, located next to each other over some sections, they form an upwardly directed feed section and a horizontal feed section for individual sheets. To achieve reliable decollation of sheets and upward feed, a suction device and holders are present, by which the actually foremost sheet is held on the upwardly feeding section of one of the conveyer belts in a frictionally engaged manner. This device also has a complicated design and is unsuitable for reliable decollation of sheets at high work capacity.
Further devices of a similar type, but which differ markedly from the subject of the present application, are the subjects of the following documents: German Patents DE 34,03,314 A1, DE 39,02,297 A1, West German Offenlegungsschrift (Laid-open Document) DE-OS 20,29,276, and West German Auslegeschrift No. DE-AS 26,28,338.
The sheet stacks to be processed with such devices of this class are often those which had passed through another machine, e.g., a copying machine, in which they had received an above-average, high electrostatic charge, and are therefore difficult to decollate, i.e., to separate from one another.